This invention relates to laser machining of a thin film to produce miniature images therein and, more particularly, to a lens array for converting the output of the laser to assure reliable and high-quality image formation in the film.
A unique compact facsimile system for transmitting a high-resolution image of a printed page is described in "An Experimental Page Facsimile System" by H. A. Watson, Bell Laboratories Record, Mar. 1975, pp. 163-169. The most important advantage of the described system is its speed - 10 seconds for scanning, transmitting and displaying the image of a standard 8 1/2.times.11-inch page.
The equipment for the described facsimile system consists of three principal parts. At the terminating end is a page-scanning apparatus which generates a video signal representing the original document. Next is a broadband analogue transmission line over which the video signal is transmitted. And finally at the receiving end there is apparatus including a laser for selectively machining a thin film and thereby reassembling an image of the document.
Advantageously, the laser included in the receiver is a gallium arsenide stripe-geometry double-heterostructure device. With such a laser it has been possible to construct a relatively compact and simple receiver for machining a thin film.
A typical gallium arsenide laser provides an optical output beam that exhibits astigmatism and an elliptical cross-section. To assure high-quality machining of the thin film it is important that the astigmatic nature of the beam be corrected and, in addition, that the beam be converted to one having a circular cross-section. Illustrative apparatus for so correcting and converting the laser beam is described in a copending application of R. G. Chemelli, D. D. Cook and R. C. Miller, application Ser. No. 599,850, filed July 28, 1975, assigned to the same assignee as this application.
A gallium arsenide laser sometimes exhibits the phenomena of beam steering and/or filamentation, effects known to workers in the art which can be especially pronounced when the laser is coupled into optical apparatus of the type described in the aforecited copending application of Chemelli, Cook and Miller. These effects can cause degradation of the images formed by gallium arsenide laser machining systems as heretofore constructed.